The present invention relates in general to devices for measuring the normal or engagement pitch of helical threads, and in particular to a device for the automatic measurement of the engagement pitch or lead of helical thread of a work piece which is fixed on a rotary work spindle of a machine whereby the helical thread of the work piece is in sliding contact with a feeler which in turn is fixed on an angularly adjustable measuring slider moving transversely to the rotary axis of the work piece and being axially displaceable relative to the latter; a sensor for generating electrical signals corresponding to the axial relative displacement between the screw-like work piece and the measuring slider is coupled to the drive for the transverse motion of the slider.
In a known device for measuring hobs used for manufacturing spur gears having involute teeth, the measuring feeler or the hob itself is moved according to an accurate predetermined gradient of the thread of the hob. In addition, prior to the sensing of the following hob cutter the feeler is manually adjusted in the direction of the base lead angle .gamma. g, for example, by moving the hob by means of a micrometer about a certain length. This manual adjustment, however, is relatively time consuming. In a further development of this known measuring device, the feeler or the hob is displaced according to an exactly determined effective pitch of the hob by means of a rolling rule which is retracted according to the base lead angle .gamma. g and thus moving the feeler in the direction of the base lead angle. The rolling rule must have a length which corresponds to the maximum length to be measured and for this reason in designing a measuring device of this type, certain construction compromises have to be made with respect to this limitation. Moreover, even in this known embodiment the time for carrying out the measurements is relatively long.